#differential

Doug writes:I have a 2007 Mercedes-Benz S550. I accidentally bought it in 2014 off eBay (long story) for about trade-in ($13,000), with 150,000 miles on the odomater. In a twist of good luck, it turned out to be a one owner car and using CarFax I was able to see and verify that it had been maintained by the selling dealer right up to a few weeks before its eBay appearance. A call to the dealer confirmed the complete service history. Even the brake pads and rotors were new, and it had a newish and very expensive set of Michelins. Almost three years later, it has been very reliable for my teen daughter and has 180,000 miles. It had a few quirks I have fixed myself (clogged charcoal canister, minor trunk leak caused by a missing rubber plug, sticking power driver seat) and only one real repair (dead stereo amp rebuilt by Becker).Now that my daughter is off at college and content with a ZipCar, I am driving it and intend to keep doing so. I have noticed a vibration in the center console area of all places, while driving around town. You feel it through your arm resting on the console lid. It’s a deep vibration, if that makes sense — coming from under the car.You don’t feel it in the seat, nor do you feel it in the steering wheel. You do not feel it at a standstill, just at 20-30 mph. It goes away at higher speeds, and the car is rock solid and smooth as glass at 75 mph. I am stumped as to the cause, and with the age of the car, I don’t want to set a dealership or even an indy shop loose on it without more of an idea of the cause. I was thinking maybe a motor mount, but it seems like I would feel that all the time, and especially at idle, which I don’t. I was wondering about maybe some kind of driveshaft or transmission mount or connection point, but it seems like a fault that would get worse with increasing speed instead of going away. Do you have any ideas?

Earlier this year I, while I was giving rides in a C7 Corvette at a racetrack, I was asked if I could give a stunning young blonde a ride around the course. Naturally, I agreed, because every middle-aged man in a Corvette wants a girl who looks exactly like that one sitting next to him. Even if we’re both wearing helmets for the whole time. Imagine my surprise when it turned out that she was a BMW auto mechanic who knew quite a bit more about cars and engines and welding and whatnot than I did.

TTAC commentator EducatorDan/PrincipalDan writes:

Long time listener, comment-er, hanger-on with another question.

I have a 2004 F150 Heritage 4×2 that just cracked the 100,000 mile mark and recently I’ve noticed a distinctive rear differential whine. It has the 4.6 V8 mod motor, 4 speed auto, and (as you can see from the pics) an aftermarket flatbed.

TTAC Commentator robstar writes:

Hello Sajeev+Piston Slap Audience,

A few weeks ago I saw something strange with my lightly-used-never-abused 2005 Subaru WRX STi — A “R. Diff Temp” started flickering on the dashboard.

Danny writes:

Ok, this may be somewhat of an abstract question, and it doesn’t really pertain to me in any particular manner, but hear me out anyway, because this sounds like one of those perfect cases of somebody (The Agonist) getting duped by a mechanic. In this case it’s the band The Agonist who travel in their “Blue Hornet” which appears to be a Chevy 1500 van. They say in the video that they dumped a bunch of money into it before they went on tour, but somewhere in California the rear differential went bad and it needed to be replaced. They go on to say in the video that they tried to get a second hand rear diff, but they were told it was illegal, so they made their way towards the border to find one closer to Mexico, where apparently these kinds of “laws” aren’t enforced. One of the band members also notes that the “rear differential decided to break again” which tells me this light of a van might not be up to the task of pulling all this gear. Maybe they should step up to a 2500, or better yet a tour bus.

Video here:

Do you know of any laws that would prohibit the installation of a second hand differential? If so, could you shed some light on why it might be illegal, or did this band simply get duped?

TTAC Commentator 67dodgeman writes:

Sajeev, I have a question for the Piston Slap expert. My son drives my old ’99 Ford Ranger (extended cab, 4 cyl, manual, 2WD) with roughly 130,000 miles on the odometer. I had new tires put on 5 months back at the Firestone place. Then last week, the anti-lock brakes started acting up. As in heavily manipulating the pedal even during very light braking. I assumed the sensor was fried and pulled the fuse, after which everything worked normally. There was a slight ticking sound from the drive train, so I replaced U-joints. Still ticking, but no other obvious issues.

Then, Friday, the driver’s side rear tire and axle came loose. Luckily he was making a low speed U-turn and the last 6” of axle was still in the housing by time he stopped. We jacked the truck up, pushed the axle back in, and pushed it home (two blocks – very very lucky it happened there and not on I-45). I pulled the differential cover and immediately found the (bleeping) C-clip loose in the housing. The anti-lock sensor works off of teeth on the ring gear (just now figured that out), so I’m assuming that having about half the teeth ground off is the cause of the brake malfunction. The oil appeared original, had that burnt smell, and was full of grit. I’m now in the process of changing the whole assembly with a salvage yard spare due to the gear damage.